1. Field of the Invention
The invention relates to the evaluation of animals, more particularly to a method and apparatus for evaluating interest of a tested animal.
2. Description of the Related Art
A conventional sucrose preference test, which was proposed by Willner P et al in 1987, is a method for measuring interest, depression degree or anti-depression therapy reaction of a tested animal, such as a mouse.
In the conventional sucrose preference test shown in FIG. 1, a tested mouse 91, which has not been fed with water for 24 hours, is contained in a housing 92 that is provided with a first dispenser 93 for dispensing non-flavored drinking water, and a second dispenser 94 for dispensing a liquid containing 2–3% of sucrose. The first dispenser 93 dispenses the drinking water at a first position that is easily accessible to the tested mouse 91 and that is at the same level as a second position at which the second dispenser 94 dispenses the liquid containing sucrose. The positions of the first and second dispensers 93, 94 are then interchanged after 30 minutes. Thereafter, amounts of the drinking water and the liquid containing sucrose consumed by the tested mouse 91 within one hour is measured, as shown in FIG. 2.
It is known in the art that the tested mouse 91 has a natural preference toward a liquid having a sweet taste. Therefore, under normal conditions, the consumed amount of the liquid containing sucrose is greater than that of the drinking water. In view of Willner's research, it is assumed that preference to sucrose is a measure of interest of the tested mouse 91, i.e., the tested mouse 91 loses interest for the liquid containing sucrose when depressed or stressed, thereby resulting in a reduced consumed amount of the liquid containing sucrose. The interest of the tested animal 91 for the liquid containing sucrose will not recover until depression or stress disappears.
However, the consumed amount of the liquid containing sucrose obtained from the conventional sucrose preference test divided by the weight of the tested mouse 91 has no distinct variation for the depressed or stressed condition, as pointed out in “Chronic Mild Stress and Sucrose Consumption: Validity as a Model of Depression”, Naida F. Forbes et al, Physiology & behavior, Vol. 60, No. 6, pp. 1481–1484, 1996. Since the first and second dispensers 93, 94 dispense respectively drinking water and the liquid containing sucrose at the first and second positions that are at the same level, the conventional sucrose preference test actually measures the preference or need of the tested mouse 91 with respect to the liquid containing sucrose. For instance, the tested mouse 91 is likely to drink more of the liquid containing sucrose when hungry, and more of the drinking water when thirsty such that the correlation between the consumed amount of the liquid containing sucrose and depression or stress cannot be verified.